Hi Robert, Baking is a huge subject!
I’ll try to give a short (and therefore incomplete and probably not very clear) version, as far as it is relevant for this case:
You are taking the information of how the light reacts, when hitting the surface of the high-poly model and use that information on a low-poly version of the wheel (that is why the retopology is necessary). This information is ‘made permanent’ (and that process is called Baking) on Images, that can be used on the low-poly model by a renderer. (What happens to the high-poly model after the Baking, won’t make a difference to how the low-poly model is being rendered.)
